1. Field of the invention
The present invention generally relates to an optical type density detector for measuring the density of a specific material contained in a material object by utilizing a difference of light absorption degree on each wavelength, which respective materials have, and more particularly relates to a portable detector for measuring a chlorophyl density contained in green leaves.
2. Description of the related art
A chlorophyl quantity contained in green leaves of a plant relates closely to do with its plant breeding and soil as well as a manuring method and a quantity of manure. Therefore, it is possible to diagnose whether or not the degree of growth of the plant is sufficient by measuring of the contained chlorophyl quantity. Thereupon, measurement of the quantity of the contained chlorophyl in the leaves is usually made to effectively provide manure, in order to promote the growth of the plant and increase a yield of the crops. A measuring method of the prior art involves, cutting a certain area in the green leaf away, and steeping it in a solvent (Acetone) for about forty-eight hours, and extracting the chlorophyl after separating it from the green leaf, and then obtaining data of the quantity of the contained chlorophyl resulting from spectrometry. There is a disadvantage that measurement by this method causes a green leaf to be hurt as well as requires spending a lot of time.
Accordingly, a device which enables the farmer to obtain data of the contained chlorophyl in a few seconds without hurting the green leaf has been put into practical use. The above-mentioned device enables the farmer to measure optically the quantity of the contained chlorophyl in the leaves with the transmitted light which comes through the green leaf at the time when an artificial light irradiates the leaf. FIG. 33 shows a basic system of chlorophyl measuring. In FIG. 33, a reference numeral 200 designates a light source such as a xenon tubing and/or a tungsten lamp. The light emitted from the xenon tubing 200 is illuminated to a sample of a leaf L through a fiber tube 201. The emitted light is transmitted through the leaf L, and the transmitted light is led to a dichroic mirror 203 through a fiber tube 202. By the dichroic mirror 203, a light belonging to the infrared region and a light belonging to the red color region are, respectively, separated from the transmitted light. The respective lights are led to the respective light receiving elements 205, 204. The respective light receiving elements measure each quantity of the respective lights. A theory of measuring a chlorophyl density is well-known and described later on. The chlorophyl density is calculated on the basis of the abovementioned respective transmitted light quantities and light quantities received at each light receiving element 204, 205 at the time when measuring without the sample.
One of the devices as described above is provided with a measuring head having a slit in which the green leaf as the sample to be measured is inserted, and a body of the device, in which both a unit for doing a computing processing for obtaining the quantity of the contained chlorophyl resulting from measuring the transmitted light which comes through the green leaf and a circuit for indicating output data from the unit are accommodated. In this device, a tungsten lamp is provided as an artificial light source. Due to utilizing the tungsten lamp, luminous intensity of the light emitted from the light source is not sufficient, so that it is necessary to provide a member isolated from a light coming from outside because the light emitted from the tungsten lamp is easily influenced by the light coming from outside. Therefore, handling of the device is troublesome.
On the other hand, another type of the device has been already disclosed. That is, the device is provided with a lamp generating a large amount of the light quantity, and a computing unit. The above-mentioned lamp as the light source is a flash tube for emitting a flashing light in order to obtain a large amount of the stabilized light, and the computing unit is so designed that a logarithmic arithmetic necessary for obtaining the quantity of the contained chlorophyl is easily carried out by inserting a damping period of the light quantity into an exponential function. Whereby, stability on an electrical circuit is improved as well as no adjustment for measurement is requested each time the device is used for measurement. However, this device has a disadvantage in that an electrical power circuit for the light source is complicated and a production cost of the device arises, as well.
Furthermore, if the lamp to be utilized in the device as the light source has a character that the quantity of the light emitted from the lamp is changing in response to an ambient temperature, the measured results do not become accurate, owing mainly to dispersion of the light quantity due to the temperature. So one point of importance for the measuring device is that the device has high reliability so that all the measured results measured by the device under any circumstances are always accurate. Another point of importance for the device is that the device can be easily utilized to make measurements. That is why something must be done not only to maintain high reliability and good operability of the device, but also to ensure simplification for the device as well as the improvement of the cost-performance for the device.